The present invention relates to a pressurizing apparatus comprising a power source including a motor and a flywheel and a slide ram adapted for linear motion through a flywheel crankshaft to pressurize a material, or more in particular to an apparatus and a method of immediately detecting an abnormal condition and promptly finding a fault such as the breakage, cracking or wear or displacement by work grip failure of a punch or die of a pressure unit which may develop during the pressurizing work by the former.
References on an abnormal load detection apparatus relating to the present invention include JP-B-59-22902 (U) filed on Nov. 17, 1981 and JP-B-57-1341 filed on Jan. 14, 1980 by Sakamura Kikai Seisakusho Ltd., a technical report entitled "Energy Sensor Developed for Extra Large Size Former" for introducing new products of Sakamura Kikai Seisakusho Ltd., and product specifications "Processa 3040-A", "Processa Model 4040" and "Processa Model 4010 Compact" of Brankamp system Peozebautomation GmbH.
The abnormal load detection apparatuses disclosed in these references are operated in such a manner that a load cell embedded in the rear part of a punch or a die records a maximum or average value of load change for each pressurizing stroke or a sync signal is used to record an average value of load change within a predetermined specific partial area in a stroke, and the resulting value thus obtained is compared with a normal value for pressurizing the work within a tolerance thereby to detect an abnoramal condition or fault.
In these conventional apparatuses, a normal value is not compared with each of load changes sampled continuously in the process of work deformation at or in the vicinity of a pressurizing point of a moving pressure unit, and therefore it is impossible to detect with high accuracy an abnormal load which may occur instantaneously at a given time point while the work is under pressure.
Another disadvantage of these conventional apparatuses is that in view of the fact that the full load is imposed on a load cell providing a sensor, it is practically impossible to use a small-capacity high-sensitivity load call capable of detecting a very small change under an abnormal load and that the use of a single data of average or maximum load for each stroke of the pressurizing work to detect a fault fails to attain an abnormal load detection with high resolution.